A new continued fraction expansion algorithm, the so-called a/b-expansion, is introduced and some of its basic properties, such as convergence of the algorithm and ergodicity of the underlying dynamical system, have been obtained. Although seemingly a minor variation of the regular continued fraction (RCF) expansion and its many variants (such as Nakada's α-expansions, Schweiger's odd-and even-continued fraction expansions, and the Rosen fractions), these a/b-expansions behave very differently from the RCF and many important question remains open, such as the exact form of the invariant measure, and the "shape" of the natural extension.